The invention relates to an arrangement or system consisting of:
a battery handle for electro-optical diagnostic instruments, one end face of the handle being provided with an aperture and the handle having a casing at least portions whereof are electrically conductive;
a charger with a connecting pin which, in the charging position, projects into the aperture of the battery handle; and
a storage cell with a positive pole which protrudes from an end face thereof and, after insertion into the battery handle, projects into the aperture of the latter.
In electro-optical diagnostic instruments, for example opthalmoscopes, otoscopes and the like, in general a so-called battery handle is provided, which serves to receive a battery or a storage cell and to hold, and supply current to the instrument formed as an attachment to the battery handle. Diagnostic instruments of the said type are used, for example, in doctors' consulting rooms or in the treatment rooms of hospitals, and they are preferentially operated with handles which are fitted with storage cells. Since, due to the required convenient size of the handles, the storage cells have only a limited capacity, it is in general recommended to re-insert the handles after each examination into the chargers provided for this purpose, so that they are always ready to operate. In practical use, however, it is frequently necessary to carry out a large number of examinations with such a handle, and in certain circumstances with different diagnostic attachments, before the storage cell can be recharged. This is the case, for example, during rounds in the hospital or during home visits by the doctor. It can then happen that the capacity of the storage cell is prematurely exhausted. For this case, it is extremely advantageous if the handle is designed in such a way that the inserted storage cell can simply be exchanged for dry batteries which are not rechargeable and which later are replaced again by the rechargeable storage cell. In the event of this exchange being forgotten for once, which can readily be imagined, battery handles of this type must be designed in such a way that, if one or more batteries have been introduced into the handle, an inadvertent connection to the charger is impossible. This is necessary in order to prevent damage to the charger or an expansion or even explosion of the batteries subjected to a charging current.
In the arrangement of the type described initially, known from U.S. Pat. No. 4,147,163, the storage cell has a greater length than the batteries which can be inserted into the handle. Within the casing, on the side of the aperture of the battery handle, a contact piece is provided which is axially displaceable under the tension of a spring and which, in the case of using batteries, forms a bridge from the battery terminal towards the electrically conductive part of the casing of the battery handle and, when a storage cell is used, interrupts the connection to the conductive part of the casing because of the greater length of the storage cell.
Such a switching mechanism is relatively complicated and constructionally expensive, and this entails not only high costs but frequently also failures of the arrangement, above all because of inadequate contact being made. Furthermore, since the electrically conductive part of the casing of the battery handle in this arrangement can only be provided on the cylindrical wall part thereof, the negative pole on the storage cell must be taken out laterally with the aid of a spring contact and, due to the necessary aperture in the cylindrical part of the insulating bush of the storage cell this causes difficulties in manufacture and with respect to the mechanical durability of the storage cell.
A further disadvantage of this arrangement is that the storage cell would in any case, because of the lateral spring contact, have to have a smaller diameter than the battery types envisaged for exchange. This considerably restricts the choice of batteries and storage cells available, because of their standardized diameters.